set1 = {'apple', 'orange', 'pear', 'banana'}
set2 = set(('facebook', 'qq', 'wechat'))
set1.add('watermelon')
set2.remove('qq')
print(set1)
print(set2)
print(len(set1))
set2.clear()
print(len(set2))
print('apple' in set1)
